1. Field of the Invention
The present invention relates to a tape guide device for use in a video tape recorder or the like.
2. Description of the Prior Art
Tape guides for use in video tape recorders or the like are roughly classified into rotary tape guides and fixed tape guides.
The rotary tape guides are advantageous in that they impose less resistance to tapes guided thereby. However, the speeds of travel of the tapes guided by the rotary tape guides tend to reflect irregularities in the rotational speeds of bearings used in the rotary tape guides. Furthermore, if the direction in which a tape travels when it is guided by a rotary tape guide is not perpendicular to the axis of rotation of the rotary tape guide, then the tape is subjected to a transverse force applied by the tape guide. The latter drawback is aggravated when the tape is transversely shifted until an edge thereof is damaged by contact with a flange of the rotary tape guide, for example. Therefore, rotary tape guides are required to be machined and assembled with high accuracy, and hence cannot be manufactured easily.
The fixed tape guides allow tapes guided thereby to run stably, but present large resistance to the running tapes.
There has been a demand for a fixed tape guide which imposes smaller resistance to a running tape. One of such fixed tape guides that meet such a demand is an air tape guide for ejecting air from small holes defined in the surface of a guide body to float a tape off the guide body for thereby reducing the resistance applied to the tape. The air tape guide is still problematic since a compressor is required as an air pressure source.
To eliminate the drawbacks of the conventional tape guides, the assignee of the present application has previously proposed an ultrasonic vibration tape guide device (see Japanese Patent Application No. 02-103627). The ultrasonic vibration tape guide device employs an ultrasonic energy to reduce resistance to a running tape while allowing the tape to run stably as with fixed tape guides. The ultrasonic vibration tape guide device is adjustable in height. The proposed ultrasonic vibration tape guide device will be described below with reference to FIG. 1 of the accompanying drawings.
The ultrasonic tape guide device, generally designated by reference numeral 1, includes a main shaft 5 mounted vertically on a base 18, and an ultrasonic vibrator 3 fixed to a guide member 2 that is supported on support teeth 7b of a cylindrical support shaft 7 of brass.
Lower and upper flanges 9, 10 are disposed in abutment against lower and upper ends, respectively, of the support shaft 7, for guiding edges of a tape wound around the guide member 2.
The main shaft 5 extends through the lower and upper flanges, 9, 10 and the support shaft 7.
A height adjustment screw 6 is fitted in an upper end of the support shaft 7, and threaded over a screw 23 formed on the upper end of the main shaft 5.
The upper flange 10 is fastened to an upper end surface of an attachment 8 by a screw 15. The lower flange 9 is fixed to a lower end surface of the attachment 8 by fixing screws 22, 24.
The attachment 8 has an ultrasonic vibrator storage space 8a defined therein which houses the ultrasonic vibrator 3 therein. As shown in FIG. 2 of the accompanying drawings, the ultrasonic vibrator space 8a is defined as a hole in the shape of a rectangular parallelpiped between side walls 8b having respective stopper insertion holes 8c defined therein.
Disc-shaped stoppers 39 made of rubber have engaging protrusions 39a fitted respectively in the stopper insertion holes 8c. The ultrasonic vibrator 3 is sandwiched between the stoppers 39 to prevent the guide member 2 from rotating with respect to the attachment 8.
The attachment 8 keeps the lower and upper flanges 9, 10 parallel to each other and spaced from each other by a distance that is about 0.1 mm larger than the length of the guide member 2.
As shown in FIG. 1, the lower flange 9 is normally urged upwardly under the bias of a coil spring 35 disposed around the main shaft 5 between the lower flange 9 and the base 18. The base 18 has a pin insertion hole 20 in which there is inserted an end of the fixing pin 22 that projects downwardly from the lower flange 9.
When the height adjustment screw 6 is turned, the guide member 2 is adjusted in height under or against the bias of the coil spring 35.
FIG. 3 of the accompanying drawings shown standing-wave vibrations caused of the guide member 2 when an AC voltage is applied to the ultrasonic vibrator 3, the standing-wave vibration being illustrated along line X--X.
In FIG. 3, dotted lines N--N represent nodes on the guide member 2 where the vibrations have zero amplitude. The nodes N on the guide members 2 are axially spaced from the ends of the guide members 2 by a distance n, and the support teeth 7b are also axially spaced from the ends of the guide member 2 by the distance n, i.e., are positioned at the nodes N.
In the example of the conventional tape guide device, as will be clear from the foregoing description, the guide member 2 sandwiched by the upper and lower flanges 9, 10 attached to the attachment 8 is adjusted in height by turning the height adjustment screw 6 that is threaded over the main shaft 5. This arrangement makes the tape guide complex in structure and the main shaft 5, the upper and lower flanges 9, 10 and the attachment 8 become complex in shape, which hinders the tape guide from becoming inexpensive.
The guide member 2 and the support shaft 7 are assembled by the engagement of the inner diameter of the guide member 2 and the outer diameters of the teeth 7a, 7b of the support shaft 7. Therefore, the inner diameter of the guide member 2 and the outer diameters of the teeth 7a, 7b are required to be machined with high accuracy in dimension. Further, the conventional tape guide becomes complex in structure and hence cannot be assembled easily, which also hinders the reduction of its cost.
Furthermore, the upper and lower flanges 10, 9 urge the PG,6 upper and lower ends, respectively, of the guide member 2 so that the vibration of the guide member 2 is caused to be attenuated. Therefore, the conventional tape guide cannot allow the tape to be guided and to run satisfactorily.